The rabid dog, Tim Johnson, is in the middle of the street directly in front of the Radley house. He needs to be stopped where he is, or else he might go down a side street where there may be unsuspecting people out. The shooter must have impeccable aim, however, because if he misses, the bullet will go straight into the Radleys' house, possibly hitting someone inside. Heck Tate knows that he is not as good a shot as Atticus, so he does not want to take a chance on missing in such a critical situation. He asks Atticus, whom he knows "was the deadest shot in Maycomb County in his time", to do the job instead.

An extremely humble man who accepts violence only as a last resort, Atticus has not picked up a gun in thirty years. His children know nothing of his reputation; he has never said a word about it to them. When Tim Johnson comes staggering up the block, Atticus recognizes the danger and tries to urge Heck Tate, the sheriff, to shoot him quickly, but Heck Tate, in evaluating the situation, concludes that they will only have one chance, and that Atticus is the better man for the job. At Heck Tate's insistence, Atticus takes the rifle, and with obvious skill fires off one shot. Apparently, Atticus's ability with the rifle has not diminished over the years, because he hits Time Johnson right above the left eye; the poor dog never even knows what hits him (Chapter 10).

Tim Johnson is aware that he is not a good shooter, but if he lets the dog get away then unsuspecting people could get hurt in another lane. Therefore, he calls Atticus because he knows Atticus's aim will be spot on. If Tim shot and missed, then he would have hit the Radley house and might hurt someone inside the house and he did not want to risk that.